FEM-simulation of high pressure discharge lamps: examples for modelling of cathode regions and of 3-D convective flow

Summary form only given, as follows. Lamps with high radiance or high luminance are getting increasing importance for projection applications, fiber based light distribution, or photolithographic applications. Such lamps must have short arcs of a few millimeters only and very high operating pressure of the lamp filling (mostly Xe, Hg, p/spl cong/5 bar, without or with dopants). Such lamps are usually operated with DC current, even if dopants are present, Because of the short electrode distance, electrode regions and arc column can no longer be clearly distinguished. The high operating pressures lead to strong convective flow within the lamp bulb, which creates strong local thermal loading of the quartz wall. Because of these problems, design and construction of such lamps require a good understanding of plasma regions close to the electrodes and of 3-dimensional convective flow patterns. The paper addresses both topics. A new approach for modelling both the LTE-plasma between the electrodes and the non-LTE-region very close to the cathode with a single set of equations is presented and FEM-results for 2-D, noncylindrical lamp geometries are discussed. 3-D convective plasma flow modelling results for different lamp pressures and lamp operating positions are also presented.